The necessity for accurate alignment of rotating shaft machinery is well known. More specifically, in order to assure maximum output and machinery longevity, accurate alignment between driving and driven components is essential. As is known in the art, if a coupling is set for perfect alignment in the "cold" (non-running) condition, the machinery will often "grow" out of this true alignment as operating temperatures change. This can lead to higher vibration levels, or even shaft misalignment severe enough to potentially result in catastrophic failure.
In order to compensate for this phenomenon, in the past cold alignment figures to which the machinery is initially set in the field may include an offset to account for relative anticipated thermal expansion or contraction. The machinery can be set out of alignment by a predetermined amount, for example, and then during operation, grow into true alignment. Often however accurate cold alignment offset figures are not available, leaving the field technician the responsibility of accurately aligning the rotating components without any guidelines for compensation. This necessarily leads to inaccuracies and possibly even machine failure. Obviously, this is unacceptable due to the possible safety hazard, damage to the machinery and of the related down time.
A variety of shaft alignment systems/techniques have been developed to date. U.S. Pat. No. 4,102,052 to Bloch discloses an apparatus for determining axial displacement or deflection of a rotating shaft or coupling, allowing compensation for shaft axial growth. A calibrated deflection decal is affixed to the coupling shaft and zeroed at some convenient point, such as the coupling guard of a standard diaphragm-type coupling. The machine is placed into service and axial deflection of the shaft is determined by reading the decal with the aid of a speed synchronized strobe light. While use of this system has proved generally effective, it provides only data of sufficient precision to aid in correcting axial displacement. This system does not address the problem of obtaining accurate enough data to correct parallel and angular misalignment, and as such is only of limited effectiveness.
U.S. Pat. No. 4,428,126 to Banks discloses an apparatus for monitoring shaft alignment utilizing a bar or other mounting means attached to the component casings. Eddy current proximity probes are utilized to obtain data which can be converted into linear alignment change figures. U.S. Pat. No. 3,783,522 to Dodd uses proximity probes mounted somewhat differently, to accomplish the same thing, i.e., measurement of alignment change. Neither system measures the basic parallel and angular alignment condition, both depending on getting this separately by other means. Also, both are subject to error due to radial growth which may occur on the machine/bearing housing to which they are mounted, in proportion to the distance of such surface from the shaft centerline. Use of this type probe system increases complexity, and can lead to inaccuracies due to the indirect method of obtaining the alignment figures.
U.S. Pat. No. 4,516,328 to Massey discloses a shaft alignment device including a relatively complicated framework. Such a device cannot be used to obtain running or hot alignment data. Similarly, U.S. Pat. No. 4,586,264 to Zatezalo discloses a shaft alignment device utilizing oppositely mounted split flanges spaced a distance from the center coupling. Oppositely mounted dial indicators are set to read radial run-out data from one flange to the other. Here again, the apparatus does not lend itself to accurate running checks.
U.S. Pat. Nos. 4,033,042 and 4,148,013 to Bently and Finn, respectively, show eddy current proximity probe systems which effectively measure running angular and parallel alignment of one machine relative to another to which it is flexibly coupled, using shaft centerline relationships. This is ideal from a mathematical standpoint, but the systems are complex, expensive, and difficult to retrofit to existing machines.
A need exists therefore, for a shaft alignment system designed to be simply installed and which can be utilized to provide both hot and cold alignment data and covering axial displacement and both angular and parallel misalignment. Such a device would be simple to install and operate, and yet provide highly accurate data results.